1. Field of the Invention
This invention relates to a mechanical seal assembly for sealing a rotary shaft to a housing having a shaft opening through which the shaft extends, and more particularly to a mechanical seal assembly having means for supplying lubrication into the annular sealing zone between the relatively rotatable seal rings to minimize film loss problems which may otherwise occur when the fluid pressure in the housing is relatively low.
2. Background Discussion
Mechanical seals depend on a thin film of the liquid that they are sealing to lubricate and cool their opposing seal faces. Conditions such as vaporization, air trapped in piping and other conditions when fluid pressure in the housing is relatively low can cause seals to lose the film with consequential damage or even complete failure. In addition, at start-up, the film is generally non-existent. It is common practice to provide a flow of liquid into the seal area to avoid the failure of the seal. Generally, liquid is injected into the seal area at a higher pressure than the fluid in the stuffing box. This adds to the expense of extra equipment and a supply of additional liquid. The injected liquid may simply be tapped from pump discharge, but this results in loss of recirculation energy and may require pressure dropping means such as orifices subject to problems of clogging and erosion. Where fluid is added, there are often considerable cost measures consequent to adding extra fluid to the process fluid being pumped. In many cases, the injected fluid is merely serving to provide turbulence and to wash away a slow buildup of gas from the stuffing box.
3. Description of the Prior Art
Heim, U.S. Pat. No. 3,236,529, issued Feb. 22, 1966, for MECHANICAL SEAL, teaches supplying lubricating fluid to the opposing seal faces of a seal by using the operating pressure of the pump discharge fluid to force some of the liquid being pumped back into the stuffing box.
Tracy, U.S. Pat. No. 3,486,760, issued Dec. 30, 1969, for MECHANICAL SEAL ASSEMBLY WITH LUBRICATING MEANS teaches supplying lubricating fluid to the opposing seal faces of a pair of seal rings through drilled passageways or bores in the non-rotatable seal ring to arcuate grooves in the non-rotatable seal ring face. A coupler connects the passageways in the seal ring to a source of lubricating fluid.
Wilk, U.S. Pat. No. 3,495,840, issued Feb. 17, 1970, for MECHANICAL SEAL START-UP LUBRICATING ARRANGEMENT teaches supplying a lubricating fluid to generally the center of the opposing seal faces of a pair of seal rings through drilled passages or bores in the non-rotatable seal ring and its back-up ring to arcuate grooves in the non-rotatable seal ring face. The fluid flows or is pumped outward across the opposing seal faces to a discharge location.
Wiese, U.S. Pat. No. 3,498,620, issued Jan. 22, 1968, for MECHANICAL SEAL LUBRICATION MEANS teaches structure similar to that taught by Wilk, supra, and adds a time-delay means for operating the fluid injection circuit to supply the lubricating fluid to the seal faces.
Lesiecki et al, U.S. Pat. No. 4,502,693, issued Mar. 5, 1985, for BUSHING SEAL WITH DUAL RESTRICTED FLUID PASSAGES teach supplying a sealing fluid at a pressure in excess o a pressure of a process fluid within the compressor structure when the compressor is not operating. The object is to keep bushing surfaces wet whenever a process gas may come in contact with a bushing surface. The sealing fluid traverses several restricted fluid passageways from its intake location to its outlet. Also provided is a bushing having radial surfaces exposed to fluid pressure which surfaces are sized to have "areas such that there is a high enough pressure unbalance across the bushing urging" a face thereof against a seal liner "to prevent axial movement of the bushing but low enough so that the bushing will not float with the shaft during operation . . . "